Parkinson's disease is a debilitating disease caused by the death of dopamine neurons in the central nervous system. Parkinson's disease patients experience life altering symptoms of tremors, slowness in moving, and difficulty walking. While no drugs exist which cure the disease or stop its progression, a number of drugs exist to help with symptoms. The most commonly used drug and the drug all Parkinson's patients eventually use is levodopa. Levodopa (also referred to herein as “levodopa”) is currently supplied in tablets with or without one or two other drugs. The other drugs typically function to prevent the body from metabolizing the levodopa before it can take its effect. Many patients initially respond well to levodopa treatment, but over time the effect becomes diminished. Patients typically start increasing their levodopa dosage as their disease progresses. A patient at the early stages of taking levodopa may only take 200 mg of levodopa per day, but a later stage patient could be taking 600 to 1200 mg of levodopa a day. Once the doses increase, patients become prone to dyskinesias. Dyskinesias are involuntary movements due to too much levodopa. When patient levodopa concentrations go to low, patients experience freezing episodes where the patient has significant difficulty moving. Once a freezing episode occurs, patient can take a tablet of levodopa, but they have to wait until the levodopa is absorbed to become unfrozen. Further complicating the freezing problem is that Parkinson's patients have poor stomach motility resulting in slow drug absorption. An inhalable formulation of levodopa could help patients with these freezing issues. A difficulty in creating an inhalable levodopa product is delivering enough dose to the patient, since levodopa is a high dose drug. Another difficulty is delivering an inhaled drug to a Parkinsons' patient. Since these patients are movement impaired, they need a quick and simple process to inhale the levodopa.
In addition to the above difficulties with delivering levodopa, a number of difficulties exist with delivering high doses of any drug by the pulmonary route. A dry powder containing a drug can vary greatly in density. Modifying the density of the powder can affect stability and the ability of the drug to reach the lungs appropriately. However, optimizing the density of the levodopa inhalable powder enables the effective delivery of high doses of levodopa to the patient by inhalation. Even if appropriate density can be reached for a high dose drug such as levodopa, the efficient emptying of the powder from the capsule is also a critical factor. If the emptying characteristics of the capsule are poor, the increased dosage achieved by optimal loading of the powder into the capsule is diminished.
A number of important challenges exist to deliver a high dose of levodopa to a Parkinson's patient while also keeping the drug product stable and easy to use for the patient. Pulmonary powders may be provided in amorphous form as amorphous forms of a compound have faster dissolution and would be more likely to show a fast onset of action. Despite the advantage of fast onset of action for an amorphous powder, amorphous powders are difficult to manufacture and difficult to keep stable under long term storage conditions, as required by the drug regulatory agencies. Further, filling large volumes of amorphous powders in a capsule can be challenging due to electrostatic charges. For crystalline powders, increasing the relative humidity can reduce the electrostatic charge of the powder and allow for better capsule filling, but increasing the relative humidity is not a viable option for an amorphous powder. Amorphous powders become prone to amorphous to crystalline transitions under elevated relative humidity. Thus, a significant difficulty exists in identifying a fast acting amorphous powder which is stable with a low electrostatic charge.